Study of conformational stability, structural, electronic and charge transfer properties of cladrin using vibrational spectroscopy and DFT calculations Swapnil Singh a , Harshita Singh a , Anubha Srivastava a , Poonam Tandon a,⇑ , Kirti Sinha a , Purnima Bharti a , Sudhir Kumar b , Padam Kumar b , Rakesh Maurya b a Department of Physics, University of Lucknow, Lucknow 226 007, India b Medicinal and Process Chemistry Division, Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow 226 031, Uttar Pradesh, India highlights  Conformational analysis has been studied in cladrin using FT-IR and FT- Raman.  Complete vibrational assignment along with PED has been presented by employing DFT.  Electronic properties studied using UV–Vis spectroscopy along with HOMO–LUMO.  Molecular stability has been analyzed using natural bond orbital (NBO).  NMR study has been performed to investigate the hydrogen bonding of the molecule. graphical abstract article info Article history: Received 30 January 2014 Received in revised form 19 April 2014 Accepted 23 April 2014 Available online 14 May 2014 Keywords: FT-IR FT-Raman UV–Vis spectroscopy NMR abstract In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxy- chromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibra- tional mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV–Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1 H and 13 C nuclear magnetic resonance spectra have been also recorded and compared with the calcu- lated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO–LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (l) and the first hyperpolarizability (b) that results in the nonlinearity of the molecule. Ó 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2014.04.182 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 522 2782653; fax: +91 522 2740840. E-mail addresses: poonam_tandon@yahoo.co.uk, poonam_tandon@hotmail.com (P. Tandon). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 615–628 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa